@Jig, the reasoning behind it is that Luther had already saved one Muggleborn from a Death Eater raid, so he must have had a reason to take that risk, so its at least worth hearing out. Of course, if they get attacked they can just mass-Apparate back to the manor before anything bad happens, and if they don't they might just get a fairly high-ranking spy!
Also, your suggestion about only the hot-headed going would be both good and bad (I checked before I posted in case I got ninja'd again ;) ). Good because it makes sense, but bad because they would likely be much less fair to Luther than the others might be. Idk, that part isn't so much my concern so you guys can figure it out :P